This study is designed to test a new experimental drug called U-100766. This drug is an antibiotic being tested for effectiveness and safety in people with pneumonia. In laboratory testing and animal testing, U-100766 kills or helps eliminate many types of bacteria that causes pneumonia, including many bacteria that are no longer eliminated by standard antibiotics that used to be effective. Whether or not U-100766 is effective in treating pneumonia in people has not yet been tested. This study will help answer that question. This study will also test two different doses of U-100766 to find out if either one might be more effective or safer.